The Advanced Television Systems Committee Vestigial Sideband (ATSC VSB) method, a U.S.-oriented terrestrial waves digital broadcasting system, is a single carrier method and uses a field sync by 312 segment unit. Accordingly, reception performance is not good at poor channels, especially at a doppler fading channel.
FIG. 1 is a block diagram of a transmitter/receiver of a general U.S.-oriented terrestrial waves digital broadcasting system according to the ATSC digital television (DTV) standards.
The digital broadcasting transmitter of FIG. 1 has a randomizer (110) for randomizing an MPEG-2 TS, an Reed-Solomon (RS) encoder (120) of a concatenated coder form for adding a parity byte to the TS to correct errors generated by channel characteristics on transmission, an interleaver (130) for interleaving the RS encoded data in a certain pattern, and a 2/3 rate Trellis encoder (140) for performing 2/3 rate Trellis encoding and 8 level symbol mapping of the interleaved data, so that error-correcting encoding of the MPEG-2 TS is performed.
Further, the digital broadcasting transmitter has a multiplexer (150) for inserting a field sync and segment sync in the error-correcting encoded data as a data format of FIG. 2, and a modulator (160) for adding a certain DigiCipher (DC) value to the data symbol inserted with the segment sync and field sync, inserting a pilot tone therein, performing pulse-shaping and vestigial sideband (VSB) modulation, up-converting them into a signal of RF channel band and transmitting them.
Accordingly, the digital broadcasting transmitter randomizes the MPEG-2 TS through the randomizer (110), the randomized data are outer-coded through the RS encoder (120) which is an outer coder, and the outer-coded data are dispersed through the interleaver (130). In addition, the interleaved data are inner-coded by 12 symbol unit through the Trellis encoder (140) and the inner-coded data are mapped with a 8 level symbol, inserted with the field sync and segment sync, inserted with the pilot tone, VSB-modulated, up-converted into a RF signal and transmitted.
Meanwhile, the digital broadcasting receiver of FIG. 1 has a tuner (not shown) for down-converting the RF signal received through a channel into a basic signal, a demodulator (210) for performing sync detection and demodulation of the down-converted basic signal, an equalizer (220) for compensating channel distortion which is generated by multipath in the demodulated signal, a Viterbi decoder (230) for correcting errors in the equalized signal and decoding the signal in symbol data, a deinterleaver (240) for rearranging the data dispersed by the interleaver (130) of the digital broadcasting transmitter, an RS decoder (250) for correcting errors and a derandomizer (260) for derandomizing the data corrected through the RS decoder (250) and outputting the MPEG-2 TS.
Accordingly, the digital broadcasting receiver of FIG. 1 down-converts the RF signal into baseband, demodulates and equalizes the down-converted signal, performs channel decoding, and restores the original signal in a reverse order of the digital broadcasting transmitter.
FIG. 2 shows a vestigial sideband (VSB) data frame of the U.S.-oriented digital broadcasting (8-VSB) system which is inserted with the segment sync and field sync. As shown in FIG. 2, one frame consists of two fields and one field consists of one field sync segment which is the first segment and 312 data segments. Further, one segment of VSB data frame corresponds to one MPEG-2 packet and consists of a segment sync of four symbols and 828 data symbols.
In FIG. 2, the segment sync and field sync are used for synchronization and equalization in the digital broadcasting receiver. That is, the segment sync and field sync are already known data between the digital broadcasting transmitter and receiver and are used as a reference signal on equalization of the receiver.
The VSB method of the U.S.-oriented terrestrial waves digital broadcasting system as shown in FIG. 1 is a single carrier method and is weak in a multipath fading channel environment. Accordingly, performance of a receiver depends on performance of an equalizer to remove multipath.
However, according to the conventional transmission frame as shown in FIG. 2, as a field sync which is a reference signal of the equalizer appears every 313 segment, the frequency of the field sync is low compared with a signal of one frame so that equalization performance decreases.
In other words, it is not easy to estimate a channel, remove multipath, and equalize a received signal using the conventional equalizer and the above mentioned known data of small quantity. Accordingly, the conventional digital broadcasting receiver has low reception performance in a poor channel environment, especially, in the Doppler fading channel environment.
Additionally, the VSB method of the U.S.-oriented terrestrial waves digital television system of FIG. 1 is a single carrier system and has the low capacity to remove multipath in the Doppler multipath fading channel. However, if the known sequence such as a field sync is used a lot, the channel is easily estimated and the equalizer easily compensated the signal distorted by multipath using the known sequence.
However, as shown in the VSB data frame of the U.S.-oriented terrestrial waves digital television system of FIG. 2, a field sync which is known data appears every 313 segment. This is so small quantity, so that the capacity to remove the multipath by using this decreases. Especially, the capacity to remove multipath in the Doppler multipath fading channels is low.